Multiple surface fracture of ceramic thermal barrier coatings under transient thermal loads
Abstract
The objective of this research is to develop a fundamental understanding of the thermal fracture process in multi-layer ceramic coatings subjected to concentrated thermal loads. This was accomplished by investigating the crack initiation and propagation process using experimental and analytical means. Controlled experiments were developed where specimens were heated and cooled under a concentrated thermal load. The appearance of multiple surface cracks was observed as damage progressed. In some cases crack deflection along the interface was also observed. These cracks were modeled and studied analytically mainly by numerical methods. The analysis showed that the presence of multiple surface cracks was beneficial in preventing the initiation of interface cracks; thus, delaying spalling. Three methods of maximizing coating life were considered, including, minimization of the peak stresses, the minimization of strain energy release rate, and the maximization of surface crack formation. The models were then used to conduct a parametric study that investigated the effects of geometry and material properties on the thermal fracture characteristics of the multi-layer coatings. One application of this research is ceramic thermal barrier coatings which are used in diesel engines to provide thermal protection for the metal parts. A better understanding of the fracture process would provide designers with the necessary tools to develop a coating with a longer life. The research results could also be applied to other multi-layer material system subjected to thermal loads.
Degree
Ph.D.
Advisors
Kokini, Purdue University.
Subject Area
Mechanical engineering|Materials science
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.